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CS 140 Lecture 19 Sequential ModulesPowerPoint Presentation

CS 140 Lecture 19 Sequential Modules

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Standard Sequential Modules

- Register
- Shift Register
- Counter

Counter

- Applications?

Counter: Applications

- Program Counter
- Address Keeper: FIFO, LIFO
- Clock Divider
- Sequential Machine

Counter

- Modulo-n Counter
- Modulo Counter (m<n)
- Counter (a-to-b)
- Counter of an Arbitrary Sequence
- Cascade Counter

D

CNT

TC

LD

Clk

CLR

Q

Q (t+1) = (0, 0, .. , 0) if CLR = 1

= D if LD = 1 and CLR = 0

= (Q(t)+1)mod n if LD = 0, CNT = 1 and CLR = 0

= Q (t) if LD = 0, CNT = 0 and CLR = 0

TC = 1 if Q (t) = n-1 and CNT = 1

= 0 otherwise

Q3 Q2 Q1 Q0

3 2 1 0

CLR

CLK

CNT

X

D3 D2 D1 D0

LD

Q2

0 0 0 0

Q0

Modulo-m Counter (m< n)

Given a mod 16 counter, construct

a mod-m counter (0 < m < 16) with AND, OR, NOT gates

m = 6

Set LD = 1 when X = 1 and (Q3Q2Q1Q0) = (0101), ie m-1

Given a mod 16 counter, construct an a-to-b counter

(0 < a < b < 15)

A 5-to-11 Counter

Q3 Q2 Q1 Q0

CLR

Clk

CNT

X

D3 D2 D1 D0

LD

Q3

(b)

Q1

0 1 0 1 (a)

Q0

Set LD = 1 when X = 1 and (Q3Q2Q1Q0) = b (in this case, 1011)

Q2 Q1 Q0

CLR

Clk

CNT

X

D2 D1 D0

LD

Q2’

Q0

Q0 Q1 Q0

Q2

Q0’

Counter of an Arbitrary Sequence

Given a mod 8 counter, construct

a counter with sequence 0 1 5 6 2 3 7

When Q = 1, load D = 5

When Q = 6, load D = 2

When Q = 3, load D = 7

Counter of an Arbitrary Sequence

Given a mod 8 counter, construct

a counter with sequence 0 1 5 6 2 3 7

K Mapping LD and D,

we get

LD = Q2’ Q0 + Q2Q0’

D2 = Q0

D1 = Q1

D0 = Q0

Counter of an Arbitrary Sequence

Example: Count in sequence 0 2 3 4 5 7 6

LD = 1 D = 2 When Q(t) = 0

LD = 1 D = 7 When Q(t) = 5

LD = 1 D = 6 When Q(t) = 7

LD = 1 D = 0 When Q(t) = 6

Through K-map, we derive

LD = Q2’ Q1’ + Q2Q0 + Q2 Q1

D2 = Q0

D1 = Q1’ + Q0

D0 = Q1’Q0

A Cascade Modulo 256 Counter

Q7,Q6,Q5,Q4

Q3,Q2,Q1,Q0

TC0

CNT

LD

CNT

LD

X

TC

TC

Clk

Clk

D7,D6,D5,D4

D3,D2,D1,D0

TC = 1 when (Q3,Q2,Q1,Q0 )=(1,1,1,1) and X=1

(Q7 (t+1)Q6 (t+1) Q5 (t+1) Q4 (t+1)) = (Q7 (t)Q6 (t) Q5 (t) Q4 (t)) + 1 mod 16

when TC0 = 1

The circuit functions as a modulo 256 counter.

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